21785421 has 8 divisors (see below), whose sum is σ = 33196864. Its totient is φ = 12448800.

The previous prime is 21785377. The next prime is 21785437. The reversal of 21785421 is 12458712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21785421 - 2¹³ = 21777229 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21785441) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 518680 + ... + 518721.

It is an arithmetic number, because the mean of its divisors is an integer number (4149608).

Almost surely, 2^21785421 is an apocalyptic number.

21785421 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21785421 is a deficient number, since it is larger than the sum of its proper divisors (11411443).

21785421 is a wasteful number, since it uses less digits than its factorization.

21785421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1037411.

The product of its digits is 4480, while the sum is 30.

The square root of 21785421 is about 4667.4855114933. The cubic root of 21785421 is about 279.2899568987.

Adding to 21785421 its product of digits (4480), we get a triangular number (21789901 = T₆₆₀₁).

The spelling of 21785421 in words is "twenty-one million, seven hundred eighty-five thousand, four hundred twenty-one".